This guide is based on Hadoop 2.7.1 and assume that we had create a user call hadoop

Setup Passphaseless SSH from NameNode to all Nodes.

1) Run the command

ssh-keygen

This command will ask you a set of questions and accepting the default is fine. Eventually, it will create a set of private key (id_rsa) and public key (id_rsa.pub) at the user directory (/home/hadoop/.ssh)